The present invention relates generally to Micro-Electro-Mechanical-System (MEMS) micromirrors and more particularly to micromirror design for dense micromirror arrays.
Dense arrays of micromirrors (also referred to herein as ‘mirrors’) using MEMS technology are finding widespread use in a variety of devices, such as, wavelength selective switches, multiplexers, optical channel blockers, projection displays, and adaptive optics. In many MEMS applications it is desirable to minimize intermirror gaps and increase the mirror fill ratio to improve optical performance. The design of a micromirror array, however, needs to balance fill ratio requirements with requirements for allowable micromirror movement, including undesired mirror movement from vibrations or excitation from external shock.
The movement of a micromirror in a mirror array can comprise in-plane and out-of-plane translations and rotations. Of these, in-plane rotation may cause significant displacement of a mirror (e.g. at a portion of the mirror far away from the axis of rotation). Such rotation may result in contact between neighboring mirrors (or other structures), and may cause mirrors to stick to each other (e.g. stiction due to their small masses and large contact areas). Such contact may cause catastrophic failure of a MEMS device.
FIGS. 1A–B illustrate prior art one-dimensional high-fill ratio micromirror arrays 100 and 110 with mirrors labeled 102-A–F and 112-A–F, respectively. The mirrors 102-A–F of the one-dimensional micromirror array 100 shown in FIG. 1A are each supported from an edge with flexing support elements (e.g. support elements 101), and are designed to tip (i.e. rotation about an axis 105). The mirrors 102-A–F may also undesirably rotate in-plane (e.g. about one of the lower corners at the location of the support elements), as illustrated with mirror 102-D, even though the support structures (e.g. 101) are designed to suppress such rotation. As shown in FIG. 1A, mirror 102-D is displaced by an amount greater than the gap width between mirror 102-D and an adjacent mirror 102-E (e.g. at corner 108, due to the in-plane rotation), resulting in contact with the adjacent mirror 102-E. Such contact can cause damage to the mirrors and failure of the mirror array.
In the prior art micromirror array 110, shown in FIG. 1B, the mirrors 112-A–F of the one-dimensional micromirror array 110 are each supported from the center of the mirror by a flexing support structure (e.g. support structure 111, shown in phantom) beneath the mirror. The mirror array design allows the mirrors 112-A–F to piston (i.e. translation out of plane) and/or tip (i.e. rotate about axis 115) and/or tilt (e.g. rotate about axis 116, for mirror 112-A). The mirrors 112-A–F may also undesirably rotate (in-plane) about the mirror's center (at the location of the support structures), as illustrated with mirror 112-D, even though the support structure is designed to suppress such rotation. As shown in FIG. 1B, mirror 112-D is displaced by an amount greater than the gap width between mirror 112-D and the adjacent mirrors 112-C and 112-E (due to the in-plane rotation) resulting in contact with the adjacent mirrors 112-C and 112-E (e.g. at corners 117 and 118, respectively). As with micromirror array 100, such contact can cause damage to the mirrors and failure of the mirror array.
FIG. 2 illustrates a prior art two-dimensional high-fill ratio micromirror array 200, with mirrors labeled 202-A-1 . . . 202-F-6. Each micromirror in the micromirror array 200 is supported from the center of the mirror by a support structure (e.g. support structure 205 for mirror 202-A-1), as similarly discussed above with reference to the mirrors shown in FIG. 1C. The mirror array design allows the mirrors 202-A-1 . . . 202-F-6 to piston and/or tip and/or tilt about the support point. The mirrors 202-A-1 . . . 202-F-6 may also undesirably rotate (in-plane) about the support point, as illustrated with mirror 202-C-5, even though the support structure is designed to suppress such rotation. As shown in FIG. 2, mirror 202-C-5 is displaced by an amount greater than the gap between the mirror 202-C-5 and adjacent mirrors 202-C-4, 202-B-5, 202-C-6, 202-D-5 (due to the in-plane rotation) resulting in contact with these adjacent mirrors 202-C-4, 202-B-5, 202-C-6, 202-D-5 (e.g. at points 206, 207, 208 and 209, respectively). As with micromirror arrays 100 and 110, such contact can cause damage to the mirrors and failure of the mirror array.